1. Field of the Invention
The present invention relates to a light emitting element and a method of manufacturing the same. More particularly, the present invention relates to a light emitting element where irregularities are formed on one surface of a crystal growth substrate, and a method of manufacturing the same.
2. Description of the Related Art
Patent Document 1 discloses a nitride-based LED where a light emitting structure made of a nitride semiconductor is provided on a front surface of a nitride semiconductor substrate. Here, a roughened region is provided on a back surface of the nitride semiconductor substrate. The roughened region is provided with a plurality of protrusions. The light generated in the light emitting structure is emitted to the outside through the roughened region.
Patent Document 2 discloses a manufacturing method of a light emitting element where a light emitting layer made of a group III nitride semiconductor is provided on one surface of a crystal growth substrate having a translucency and a surface of the crystal growth substrate, which is an opposite surface of the surface having the light emitting layer provided thereon, is an emitting surface from which the light of the light emitting layer is emitted. This method includes an irregularities forming process for forming irregularities in at least the emitting surface of the crystal growth substrate provided with the light emitting layer, a protective film forming process for forming a protective film on at least the emitting surface of the crystal growth substrate provided with the light emitting layer, a scribe groove forming process for forming a dicing scribe groove, by a laser, in the crystal growth substrate having the protective film formed on the emitting surface, a contaminant removing process for removing contaminants adhering to an inner surface of the scribe groove in the scribe groove forming process, and a protective film removing process for removing the protective film after the contaminant removing process.
Patent Document 1: JP-A-2012-231122
Patent Document 2: JP-A-2007-142277
Conventionally, a technique has been known which is capable of improving a light extraction efficiency of a light emitting element by forming irregularities (roughened region) on one surface of a crystal growth substrate, which is an opposite surface of a surface on which a semiconductor layer constituting a light emitting element structure is formed (e.g., see Patent Document 1 and Patent Document 2).
When manufacturing the light emitting element, there has been used a method of dividing a wafer of the stacked crystal growth substrate into a plurality of light emitting elements and then forming irregularities on one surface of the crystal growth substrate for each of the light emitting elements (e.g., see Patent Document 1). However, this method has a problem of low productivity because it takes a lot of man-hours.
Accordingly, in order to improve productivity, there has been used a method of forming the irregularities on one surface of the wafer of the crystal growth substrate and then dividing the wafer of the stacked crystal growth substrate into a plurality of light emitting elements by a scribe breaking.
When dividing the wafer of the stacked crystal growth substrate into a plurality of light emitting elements, a breaking blade of a breaking device is pressed against one surface of the crystal growth substrate.
At this time, when the irregularities are formed on one surface of the crystal growth substrate, the breaking blade is deviated by the irregularities and therefore the contact position of the breaking blade is not determined. Accordingly, the load from the breaking blade is not properly applied to a dividing line portion of the crystal growth substrate. Consequently, there is a problem that separation failure (dividing failure) is liable to occur. That is, the crystal growth substrate may be divided at a portion other than the dividing line portion or the cross-section of the crystal growth substrate may be slanted and broken.
When the crystal growth substrate is a gallium nitride substrate, the gallium nitride substrate has a light transmittance lower than a sapphire substrate generally used. Accordingly, it is required to cause the gallium nitride substrate to be thinner in order to improve the light extraction efficiency of the light emitting element. However, the separation failure is liable to occur especially in the thinned gallium nitride substrate.
Further, the thinned gallium nitride substrate is liable to be damaged. Accordingly, there is also a problem that the handling such as the tape transfer is difficult to perform.
Further, when dividing the wafer of the stacked crystal growth substrate into a plurality of light emitting elements, a wafer fixing tape is adhered to one surface (exposed surface) of the crystal growth substrate. However, the adhesion of the wafer fixing tape is damaged when irregularities are formed on one surface of the crystal growth substrate. Accordingly, there is a problem that the light emitting element is liable to be separated from the wafer fixing tape.
Further, when feeding the light emitting element by a collet in order to mount the light emitting element on a mounting substrate, one surface (exposed surface) of the crystal growth substrate is absorbed by the collet. However, the absorption is deteriorated when the irregularities are formed on one surface of the crystal growth substrate. Accordingly, there is a problem that the light emitting element is liable to be separated from the collet.
Further, when bonding the light emitting element to a wiring pattern formed on the mounting substrate, it is required to apply load on one surface (exposed surface) of the crystal growth substrate. However, in this case, there is a problem that the irregularities are liable to be damaged by the application of the load when the irregularities are formed on one surface of the crystal growth substrate.